1. Field of the Invention
The present invention relates to a positional indicator used in a digitizer tablet, and more particularly to a pen-like device that can detect pen press pressure or that comprises pen pressure sensitive mechanisms.
2. Description of the Prior Art
Currently, widely used computer input devices include the keyboard and the mouse. Due to the advances of digital technologies, more and more computer users have begun working with digitizer-based devices such as digitizer tablets, which allow a user to write and draw upon the working area of the tablet and have the signals and codes interpreted by a computer. Specifically, the working area of the tablet provides a writing surface for capturing the position, pressure and key status of an object, such as a pen or a mouse, and information related to pressure and actuated keys etc. In cooperation with the tablet, a pen-like device is required to create such objects. Most existing pen-like devices, which can be corded or cordless, are not able to generate lines with variable width according to different depressed forces upon the working area of the tablet applied by the pen-like devices. To overcome this shortage, pressure sensitive pens were invented.
FIG. 1A shows a schematic cross-sectional view of a prior pressure sensitive pen 10, which comprises a casing 12 having a cylindrical outer body, a core body 14 provided on the axis of the casing 12, a ferrite core 16 having a through-hole for slidably housing the core body 14, coil 20 wound around the ferrite core 16, a movable magnetic body 18 that can move in relation to the core body 14, a spring 22, and a capacitor 24. The core body 14 has a generally cylindrical form, while its upper neighboring portion, which touches the positional detecting plane, has a tapered form such that the operation allows it to easily indicate a specified point.
The ferrite core 16 is fixed to the casing 12. The core body 14 moves backward along its axis by a depressing force when the pen top 13 is depressed against the positional detecting plane. The moveable magnetic body 18 is positioned to move in conjunction with the core body 14. The relative distance to the ferrite core 16 is therefore varied as the magnetic body 18 moves. The coil 20 and the capacitor 24 form a resonant circuit. Conditions of this resonant circuit are determined such that the circuit resonates with the coil 20 while inducing and transmitting an electromagnetic field between them. The inductance of the coil 20 can be changed when the gap between the ferrite core 16 and the magnetic body 18 is changed. It thus detects the depressing force against the pen top 13 by sensing the change in the resonant conditions caused by the placement of the pen.
However, if the pressure sensitive pen 10 is operated in an inclined position against the detecting plane, the direction of the depressing force is then no more coincident with the axial direction of the core body 14. In such a case, only the axial component of the depressing force is transferred to the core body 14 so that the amount of the depressing force contributing to detection is decreased. Thus, the inductance change generated by the displacement of the magnetic body is reduced. The sensitivity of the pen pressure detection is also reduced if the pressure sensitive pen 10 is operated in an inclined position so that it cannot detect a weaker pen pressure.
Normally, it is natural for an operator to hold the pen in an inclined position, rather than in an orthogonal position while inputting with the pen in hand onto a horizontal plane.
To attain an increased absolute sensitivity by compensating for such a defect, it is desirable to provide a structure that provides the movable magnetic body 18 with a larger area, and has its end face opposed to the face of the fixed magnetic body 16, such as shown in FIG. 1B rather than to use the movable magnetic body 18 having a smaller area shown in FIG. 1A. In FIG. 1B, it is however required to assemble the pen with the initial gap predetermined as the interval between the two magnetic bodies when the pen not depressed by its tip. That requires high accuracy when placing the movable magnetic body. Moreover, ferrite material normally used for the fixed magnetic body is made by powder metallurgy, so that its dimensional tolerance is large and thus it is difficult to ensure the accuracy mentioned above.
Accordingly, it is an intention to provide an improved pressure sensitive pen to overcome the drawbacks mentioned-above.
It is one objective of the present invention to provide a pressure sensitive pen, which uses a fixed magnetic body having one coil formed of at least a wire wound around and a movable magnetic body. A predetermined distance between the fixed magnetic body and the movably magnetic body is changed when applying a depressing force on a core body of the pen. As a result, an inductance generated by the coil is changed and a frequency of electromagnetic field emitted from the pen is thereby changed.
It is another objective of the present invention to provide a pressure sensitive pen, which utilizes an annular member disposed in a hollow cylinder to separate a fixed magnetic body having one coil formed of at least a wire wound around and a movable magnetic body such that a predetermined distance between the fixed magnetic body and the movable magnetic body is accurately and properly controlled when there is no force applied on a core body of the pen. An initial frequency of electromagnetic field emitted from the pen is kept constant and not influenced by a common difference of the magnetic bodies in dimension.
It is a further objective of the present invention to provide a pressure sensitive pen, in which one coil is formed of at least a wire wound around a fixed magnetic body so that the coil obtains a high Q value. Hence, the capability of the coil for inducing/emitting electromagnetic field is very excellent. The pen can directly induce an electromagnetic field coming from an underlying tablet to serve as power source, and does not require an additional power supply such as a battery.
It is still a further objective of the present invention to provide a pressure sensitive pen, in which one coil is formed of at least a wire wound around a fixed magnetic body so that the coil obtains a high Q value. Hence, the capability of the coil for emitting electromagnetic field is very excellent. As a result, an underlying tablet for detecting pressure variation of the pen has a higher S/N ratio, and the resolution of the tablet is improved. The signal transformation of the tablet from a frequency value into a pressure value is facilitated.
In order to achieve the above objectives of this invention, the present invention provides a pressure sensitive pen having a pressure sensitive mechanism. The pressure sensitive mechanism comprises a supporting member, an elastic element, a hollow cylindrical body, a first magnetic body, a second magnetic body, a sliding member, a core body and one coil formed of at least a wire wound around the first magnetic body. One end of the supporting member is provided with a first housing. The elastic element is disposed in the first housing. One end of the hollow cylindrical body is leaned against the end of the supporting member having the first housing. The hollow cylindrical body has an inner surface and an outer surface. The inner surface of the hollow cylindrical body is formed with an annular member for dividing the hollow cylindrical body into a second housing and a third housing. The third housing is formed between the annular member and the first housing. The first magnetic body is provided with a first central through-hole. One end of the first magnetic body is engagely received in the second housing and against the annular member. The second magnetic body is provided with a second central through-hole. The second magnetic body is movably disposed in the third housing and one end thereof is leaned against the annular member. The sliding member is movably disposed in the third housing. The sliding member is formed with a cylindrical body and an annular element. The annular element is formed around an outer surface of the cylindrical body to divide the sliding member into a first part and a second part. The length of the first part is a little shorter than that of the second magnetic body. A fourth housing is formed within the first part of the sliding member. The first part of the sliding member engagely passes through the second central through-hole of the second magnetic body such that the sliding member moves upward and downward in conjugation with the second magnetic body. The sliding member has a second end against the elastic element. The core body passes through the first central through-hole of the first magnetic body and the annular member and one end thereof is engagely received in the fourth housing. The coil formed of at least a wire is wound around the first magnetic body. When a force is upward applied on the core body, the sliding member in conjugation with the second magnetic body move upward away from the annular member. When there is no force applied on the core body, the elastic element forces the sliding member in conjugation with the second magnetic body against the annular member.